1. Field of the Invention
The invention relates to a memory system for non-volatile data storage and, more particularly, to a memory system that provides reading and programming with high density.
2. Description of the Related Art
Memory cards are commonly used to store digital data for use with various products (e.g., electronic products). Typically, these memory cards are non-volatile memories which are very popular and useful because they retain data even after being powered-off. Examples of memory cards are flash cards that use Flash type or EEPROM type memory cells to store the data. Flash cards have a relatively small form factor and have been used to store digital data for products such as cameras, hand-held computers, set-top boxes, hand-held or other small audio players/recorders (e.g., MP3 devices), and medical monitors. A major supplier of flash cards is SanDisk Corporation of Sunnyvale, Calif.
These memory cards are increasingly called on to store greater and greater amounts of data. Consequently, individual storage elements within these memory cards have been developed to support multiple levels so as to effectively store multiple bits of data. Traditional storage elements store only two states, while multiple level or high density storage elements store more than two states (e.g., four states).
Besides increasing storage capacities of memory cards, there is also a continuing need to provide higher and higher performance operation. Namely, there is a need to improve the speed by which data can be read from or written to a memory card. Since the reading or programming of memory cells within memory is able to be performed with some degree of parallelism, the improved performance can come through increased parallelism. However, increased parallelism is not merely a matter of increasing hardware components, instead precise cells control and management of inter bit line interference must be considered. However, to obtain increased parallelism requires consideration of many complex characteristics of the memory cards, such as precise cell control and inter bit line interference.
Thus, there is a need for improved approaches to reading or writing data to a memory array with a greater degree of parallelism.